2017 Revised Classification of Seizures

Clinical Article

December 22, 2017

In 2017, the International League Against Epilepsy (ILAE) released a new classification of seizure types to make diagnosing and classifying seizures more accurate and easier. Some additional seizure types have also been added allowing flexibility when diagnosing. In this article, you will find the new general outline of seizure classification compared to the old classification formulated in 1981. Additional information can also be accessed through the Epilepsy Foundation internet portal.

Previous Seizure Classification
Seizures were formerly termed as partial or generalised seizures, determined by the area or side of the brain where the seizure first initiated. Partial seizures were further broken down to simple partial or complex partial depending on whether a person is aware or conscious during a seizure. However, this classification system did not acknowledge that some seizure types such as tonic and myoclonic seizures can be either focal or generalised.

New Classification
The new basic classification is based on three key features:

*Seizures may be unclassified due to inadequate information or inability to place in other categories.

1. Where Seizures BeginFirstly, a health professional should determine the type of seizure based on whether the seizure begins in part of the brain or affects the whole brain at once. Accurate diagnosis of seizure type is crucial to guide the choice of pharmacological treatment, the possibility of surgery, prognosis, and potential causes.

Table 2. Where seizures begin

New Classification

Definition

Old Classification

Focal seizures

Start in an area or network of cells on one side of the brain

Partial seizures

Generalised seizures

Involves a network of both sides of the brain at onset

Primary generalised

Unknown onset

Unknown cause at time of onset but can change once the seizures become clear

—

Focal to bilateral tonic-clonic seizures

A seizure that starts on one side then moves to both sides

Secondary generalised tonic-clonic seizures

2. Level of AwarenessThe new ILAE guidelines split focal seizures into two groups based on the level of awareness during a seizure episode. This is an important distinction as the level of awareness is one of the main factors that affects a person’s safety during a seizure.

Table 3. Level of awareness experienced during seizures

New Classification

Definition

Old Classification

Focal aware

Patient is aware of the seizure

Simple partial

Focal impaired awareness

Impaired awareness, even if the idea of what is happening is vague

Complex partial seizures

Awareness unknown

This is due to the absence of an observer

—

Generalised seizures

This type of seizure is documented to affect awareness. Therefore, no further classification was required.

—

3. Other FeaturesThese symptoms can occur during or before the onset of seizures as shown in Table 4.

Experience other symptoms before onset of seizures, change in sensation and emotions

—

Generalised motor seizure (tonic-clonic seizures)

Seizure characterised by stiffening and jerking movements

Grand mal

Generalised non-motor seizure (absence seizures)

Seizure characterised by changes in awareness such as staring and repeated movements like lip-smacking

Petit mal

Unknown Onset SeizuresWhen the onset of a seizure is not determined, a classification of unknown onset can be applied to seizures with motor and non-motor features. Patients diagnosed with seizures of unknown onset may be reclassified later if the onset of the seizures becomes apparent.